Oddworld: Munch's Oddysee on the GBA takes a mediocre, tech demo of a game, and puts it on a console not even half as powerful. The result is under whelming, as you are left with only the core gameplay mechanics of the Xbox version, which weren't all that impressive to begin with.
This said, Oddworld hasn't been "dumbed down" or anything similar for its handheld debut, and all the complex options offered on the Xbox original (including communicating with your fellow Mudokons) fit snugly within the GBA control scheme. This in turn paves the way for complex problem solving and puzzles, which are at the heart of the Oddworld series.
Problem is, Oddworld's gameplay wasn't all that compelling when it was on the Xbox, though its beautifully rendered graphics bought it some slack. Munch and Abe get no such leniency on the GBA, where the graphics are obviously nowhere near as impressive. The title does look fairly competent for a handheld title, but not to the level where its tedious and repetitive puzzles can be excused. There are also a few repetitive voice clips, but these are not enough to bring the game's presentation up to par.
Oddworld: Munch's Oddysee on the Xbox was a game that squeaked by on visual polish alone. Stripped of its pretty clothing, it's a frail shell of a game, and not worth your money.
-George